Promotion of mycorrhiza formation and growth of willows by the bacterial strain <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. 23L on fly ash

Re-vegetation of fly ash, the principal by-product of coal fired power stations, is hampered by its unfavourable chemical and physical properties for plant growth. In the present study, we evaluated the use of inoculation with a mycorrhiza-associated bacterial strain (Sphingomonas sp. 23L) to promote mycorrhiza formation and plant growth of three willow clones (Salix spp.) on fly ash from an over-burdened dump in a pot experiment. The high pH_H2O (8.7) and low nitrogen content (N_t = 0.1 g kg⁻¹) in combination with hydrophobicity of the particle surfaces caused low plant growth. Inoculation of the willows with Sphingomonas sp. 23L improved the nitrogen uptake by plants, increased plant growth and stimulated formation of ectomycorrhizae with an autochthonous Geopora sp. strain on all three willow clones. The ectomycorrhiza formed by the Geopora sp. was morphologically and anatomically described. The inoculation significantly increased the shoot growth of two Salix viminalis clones and the root growth of a S. viminalis x caprea hybrid clone. We conclude that inoculation with mycorrhiza promoting bacterial strains might be a suitable approach to support mycorrhiza formation with autochtonous site-adapted ectomycorrhizal fungi in fly ash and thereby to improve re-vegetation of fly ash landfills with willows.     

Association of Azospirillum brasilense with pearl millet (Pennisetum americanum (L.) Leeke)

Summary Microscopic observations of the root system of pearl millet (Pennisetum americanum (L.) Leeke) var. BJ 104 after surface sterilization and incubation in phosphate malate triphenyl tetrazolium chloride (TTC) revealed extensive colonization by Azospirillum spp. when plants were grown in sterile, partially sterile and field conditions as evidenced by the TTC-reducing property of active cells of the bacterium. Quantitative studies showed the need to standardize the techniques further to ensure more precise monitoring of the bacteria in the rhizosphere, as large numbers of soil bacteria were found capable of growth on specific media, thus interfering with the plate counts. Seed inoculation with A. brasilense increased the mean grain yield of pearl millet under different agroclimatic conditions in India. The mean increase in grain yield due to inoculation over uninoculated controls was also noticed with graded levels of fertilizer nitrogen (urea). Inoculation alone contributed to increased nitrogen uptake of plants with varying levels of fertilizer nitrogen application under sandy loam soil conditions (pH 7.3). The effects of inoculation were more prominent under lower levels of nitrogen than at the higher levels. The root biomass under field conditions was increased with Azospirillum spp. inoculation at 10 and 20 kg N/ha than their corresponding uninoculated controls.     

Seed inoculation with <Emphasis Type="Italic">Bacillus</Emphasis> spp. improves seedling vigour in oil-seed plant <Emphasis Type="Italic">Jatropha curcas</Emphasis> L.

Jatropha (Jatropha curcas L.) is a non-edible oil-seed plant with adaptability to marginal semi-arid lands and wastelands. The Indian Government is promoting jatropha to reduce dependence on the crude oil and to achieve energy independence by the year 2012, under the National Biodiesel Mission. Selected strains of Bacillus spp., either supplemented with or without chitin, were tested for their ability to promote growth of jatropha seedlings in pot culture studies. The strains supported growth of jatropha seedlings up to 42 days after sowing. Among all strains, Bacillus pumilus (IM-3) supplemented with chitin showed over all plant growth promotion effect resulting in enhanced shoot length (113%), dry shoot mass (360%), dry root mass (467%), dry total plant mass (346%), leaf area (256%), and chlorophyll content (74%) over control. Treating seeds with strain IM-3 without chitin resulted in enhanced dry shoot mass (473%), dry total plant mass (407%), and chlorophyll content (82%). However, Bacillus polymyxa (KRU-22) with chitin supported maximum root length (143%). Either strain IM-3 alone or in combination with other promising strains could be promoted further for enhanced initial seedling growth of jatropha.     

Cucumber performance is improved by inoculation with plant growth-promoting microorganisms

We investigated the effects of inoculation of Rhodobacter sphaeroides, Lactobacillus plantarum, and Saccharomyces cerevisiae on cucumber plant growth promotion and on the contents of plant hormones, amino acids, and mineral nutrients. We showed that treatment with all three bio-inoculants significantly increased the shoot length, root length, shoot fresh weight, shoot dry weight, and chlorophyll content, via secretion of indole acetic acid and/or organic acids. Inoculation with R. sphaeroides had more favorable effect on plant growth than did inoculation with L. plantarum or S. cerevisiae, by significantly enhancing the gibberellin and reducing the abscisic acid contents. The results of amino acid analysis revealed that inoculation with R. sphaeroides, L. plantarum, and S. cerevisiae generally increased the contents of 17 amino acids, namely, aspartic acid, threonine, serine, glutamic acid, glycine, alanine, cysteine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, arginine, and proline. With the exception of cysteine, all these amino acids were present in higher concentrations in plants inoculated with R. sphaeroides than in control plants or in plants inoculated with L. plantarum and S. cerevisiae. Furthermore, inoculation with R. sphaeroides significantly increased the calcium, potassium, magnesium, and phosphate contents. Our results suggest that the use of R. sphaeroides, L. plantarum, and S. cerevisiae in agricultural fields can improve plant growth. Moreover, inoculation of cucumber plants with R. sphaeroides regulates plant functional metabolites, thereby promoting plant growth.     

Effect of plant growth-promoting bacteria and soil compaction on barley seedling growth, nutrient uptake, soil properties and rhizosphere microflora

Inoculants are of great importance in sustainable and/or organic agriculture. In the present study, plant growth of barley (Hordeum vulgare) has been studied in sterile soil inoculated with four plant growth-promoting bacteria and mineral fertilizers at three different soil bulk densities and in three harvests of plants. Three bacterial species were isolated from the rhizosphere of barley and wheat. These bacteria fixed N₂, dissolved P and significantly increased growth of barley seedlings. Available phosphate in soil was significantly increased by seed inoculation of Bacillus M-13 and Bacillus RC01. Total culturable bacteria, fungi and P-solubilizing bacteria count increased with time. Data suggest that seed inoculation of barley with Bacillus RC01, Bacillus RC02, Bacillus RC03 and Bacillus M-13 increased root weight by 16.7, 12.5, 8.9 and 12.5% as compared to the control (without bacteria inoculation and mineral fertilizers) and shoot weight by 34.7, 34.7, 28.6 and 32.7%, respectively. Bacterial inoculation gave increases of 20.3–25.7% over the control as compared with 18.9 and 35.1% total biomass weight increases by P and NP application. The concentration of N and P in soil was decreased by increasing soil compaction. In contrast to macronutrients, the concentration of Fe, Cu and Mn was lower in plants grown in the loosest soil. Soil compaction induced a limitation in root and shoot growth that was reflected by a decrease in the microbial population and activity. Our results show that bacterial population was stimulated by the decrease in soil bulk density. The results suggest that the N₂-fixing and P-solubilizing bacterial strains tested have a potential on plant growth activity of barley.     

Influence of a plant growth-promoting pseudomonad and vesicular-arbuscular mycorrhizal fungus on alfalfa and birdsfoot trefoil growth and nodulation

Summary In a growth chamber study we examined the influence of a plant growth-promoting rhizobacterium, Pseudomonas putida R-20, and an acid-tolerant vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices 25, on Medicago sativa L. and Lotus corniculatus L. growth and nodule development. Seedlings were planted in an acidic (pH 5.5), P-deficient soil containing re-established native microflora (minus VAM) and appropriate rhizobia, and inoculated with the rhizobacterium, the VAM fungus, or both. The plants were assayed at three intervals for up to 10–11 weeks. The growth-promoting rhizobacteria alone increased alfalfa shoot mass by 23% compared to all other treatments, but only at 8 weeks of growth, apparently by promoting nodulation and N₂ fixation (acetylene reduction activity). The presence of VAM, either alone or in combination with the rhizobacteria, generally decreased root length but only at 8 weeks also. As a group, the inoculation treatments increased all nodular measurements by 10 weeks of growth. Few treatment effects were found at 7 and 9 weeks for birdsfoot trefoil; neither plant nor nodular measurements differed among treatments. By 11 weeks, shoot mass was increased by the rhizobacteria alone by 36% compared to the control. As a group, the inoculation treatments all showed increased nodular responses by this time. The rhizobacteria stimulated mycorrhizal development on both plant species, but only at the initial samplings. No synergistic effects between the plant growth-promoting rhizobacterium and VAM inoculation were found. Although these results lend credence to the concept of managing microorganisms in the rhizosphere to improve plant growth, they emphasize the necessity for a more thorough understanding of microbial interactions as plants mature.     

Biological nitrogen fixation in Azospirillum strain-maize genotype associations as evaluated by the 15N isotope dilution technique

Few studies of the inoculation of cereal crops with N₂-fixing bacteria have included more than one or two plant genotypes. In a recent study performed in Argentina using 12 different maize genotypes, it was found in 2 consecutive field experiments that several of them responded consistently, either negatively or positively, to inoculation with a mixture of strains of Azospirillum spp. The present study in post was performed to investigate the effect of inoculation of individual strains (and a mixture) of Azospirillum spp., and their nitrate reductase negative (NR-) mutants, on the growth of four of these maize genotypes. Two of these genotypes were grown in ¹⁵N-labelled soil with the aim of quantifying any contributions of biological N₂ fixation. Two genotypes (Morgan 318 and Dekalb 4D-70) produced similar increases in grain yield when they were inoculated with a mixture of Azospirillum spp. strains or fertilized with the equivalent of 100 kg N ha^-1. The other genotypes (Dekalb 2F-11 and CMS 22) showed little response to inoculation or N fertilization. The Morgan 318 and Dekalb 4D-70 genotypes showed a large increase in total N accumulation, suggesting that the response was due to increased N acquisition, but not due to bacterial nitrate reductase as the NR- mutants generally caused plant responses similar to those of the parent strains. Despite problems with the stabilization of the ¹⁵N enrichment in the soil, the ¹⁵N isotope dilution results indicated that there were very significant biological nitrogen fixation (BNF) contributions to the Dekalb 4D-70 and CMS 22 maize genotypes.Dedicated to Professor J.C.G. Ottow on the occasion of his 60th birthday     

Does plant growth phase determine the response of plants and soil organisms to defoliation?

To test a hypothesis that the effects of defoliation on plant ecophysiology and soil organisms depend on the timing of defoliation within a growing season, we established a greenhouse experiment using replicated grassland microcosms. Each microcosms was composed of three plant species, Trifolium repens, Plantago lanceolata and Phleum pratense, growing in grassland soil with a diverse soil community. The experiment consisted of two treatment factors—defoliation and plant growth phase (PGP)—in a fully factorial design. Defoliation had two categories, i.e. no trimming or trimming a total of four times at 2 week intervals. The PGP treatment had four categories, i.e. 1, 3, 7 or 13 weeks growth following planting before the first defoliation (subsequently referred to as PGP1, PGP2, PGP3 and PGP4, respectively). In each PGP treatment category, microcosms were harvested 1 week after the final defoliation. Harvested shoot and root mass and total shoot production (including trimmed and harvested shoot mass) increased with time and were lower in defoliated than in non-defoliated systems. The fraction of root biomass of harvested plant biomass decreased with time but was increased by defoliation at PGP3 and PGP4. The proportion of T. repens in total shoot production increased and those of P. lanceolata and P. pratense decreased with time. Defoliation increased the proportions of P. lanceolata and P. pratense in total shoot production at PGP3 and PGP4. Root N and C concentrations increased and root C-to-N ratio decreased with time in non-defoliated systems. Defoliation increased root N concentration by 38 and 33% at PGP1 and PGP2, respectively, but decreased the concentration by 22% at PGP4. In contrast, defoliation reduced root C concentration on average by 1.5% at each PGP. As with the effects on root N concentration, defoliation decreased the root C-to-N ratio at PGP1 and PGP2 but increased the ratio at PGP4. Among soil animal trophic groups, the abundance of herbivorous nematodes was higher at PGP4 than at PGP1-3 and that of predacious nematodes higher at PGP2-4 than at PGP1, while the abundance of bacterivorous, fungivorous and omnivorous nematodes and that of detritivorous enchytraeids did not differ between the PGP categories. Among bacterivorous nematodes, however, Acrobeloides, Chiloplacus and Protorhabditis species decreased and that of Plectus spp. increased with time. Defoliation did not affect the abundance of soil animal trophic groups, but reduced the abundance of herbivorous Coslenchus spp. at each PGP and raised the abundance of herbivorous Rotylenchus spp. and bacterivorous Eucephalobus spp. at PGP4. Confirming our hypothesis, the results suggest that the effects of defoliation on the attributes of grassland plants, such as biomass allocation between roots and shoots and root quality, may depend on the timing of defoliation within a growing season. However, contradicting our hypothesis, the results suggest that significant changes in plant attributes after defoliation may not always lead to substantial changes in the abundance of belowground organisms.     

Influence of Pseudomonas syringae R25 and P. putida R105 on the growth and N2 fixation (acetylene reduction activity) of pea (Pisum sativum L.) and field bean (Phaseolus vulgaris L.)

The effects of inoculating field peas (Pisum sativum L.) with Rhizobium leguminosarum and field beans (Phaseolus vulgaris L.) with R. phaseoli, alone or in combination with Pseudomonas syringae R25 and/or P. putida R105, were assessed under gnotobiotic conditions in growth pouches and in potted soil in a growth chamber. Inoculation of peas with P. syringae R25 or P. putida R105 alone had no effect on plant growth in pouches. In soil, however, the isolate R25 inhibited nitrogenase activity (as assessed by acetylene reduction assay) of nodules formed by indigenous rhizobia; strain R105 stimulated pea seedling emergence and nodulation. P. syringae R25 inhibited the growth of beans in either plant-growth system. P. putida R105, however, had no effects on beans in pouches, but reduced plant root biomass and nodulation by indigenous rhizobia in soil. Coinoculation of pea seeds with R. leguminosarum and either of the pseudomonads significantly (P<0.01) increased shoot, root, and total plant weight in growth pouches, but had no effect in soil. Co-inoculation of field beans with R. phaseoli and P. putida R105 had no effects on plant biomass in growth pouches or in soil, but the number of nodules and the acetylene reduction activity was significantly (P<0.01) increased in the soil. In contrast, co-inoculation of beans with rhizobia and P. syringae R25 had severe, deleterious effects on seedling mergence, plant biomass, and nodulation in soil and growth pouches. Isolate R25 was responsible for the deleterious effects observed. Although plant growth-promoting rhizobacteria may interact synergistically with root-nodulating rhizobia, the PGPR selected for one crop should be assessed for potential hazardous effects on other crops before being used as inoculants.     

Effect of inoculation with different strains of Azospirillum brasilense on cotton (Gossipium barbadense)

Summary The response of the cotton plant to inoculation with six strains of Azospirillum brasilense was investigated under subtropical conditions in Egypt. Azospirilla populations and activities were increased as a result of root inoculation with liquid inoculum of Azospirillum sp. Highest C₂H₂ — reduction activities on roots were obtained with strains S631 and Sp Br 14 (means of 216.85 and 209.50 nmol C₂H₄g^–1 root h^–1 respectively) while strain M4 gave the lowest activity (mean of 100.8 nmol C₂H₄g^–1 root h^–1). Statistical analysis showed that Azospirillum strains 5631, Sp Br 14, E15 and SC22 significantly increased the plant dry weight and nitrogen uptake while inoculation with strains M4 and SE had no significant effect in that respect.     

Synergistic effect of inoculating plant growth-promoting Pseudomonas spp. and Rhizobium leguminosarum-FB1 on growth and nutrient uptake of rajmash (Phaseolus vulgaris L.)

Plant growth-promoting bacteria (PGPB) Pseudomonas lurida-NPRp15 and Pseudomonas putida-PGRs4 possessing multiple plant growth-promoting traits were isolated from rhizoplane of pea and rhizosphere of garlic, respectively. The effects of individuals and combinations of Pseudomonas spp. with effective root nodulating symbiotic nitrogen fixing Rhizobium leguminosarum-FB1 on plant growth, nutrient uptake and yield of the rajmash plant were studied under greenhouse conditions. Bacterial inoculation resulted in significantly higher values for plant dry biomass, N, P, K, Zn and Fe contents as compared to the uninoculated control. Furthermore, dual inoculation of P. lurida-NPRp15 with R. leguminosarum-FB1 significantly increased root and shoot dry weight, nodulation, nutrient uptake, pod yield, and nutrient content of pods of rajmash VL63 compared to controls, single and triple inoculation. The results of the study indicate the potential of harnessing the benefit of plant growth-promoting and nitrogen-fixing microorganisms to improve the growth and yield of rajmash.     

Genetics and molecular biology of Azospirillum

 Genetic manipulation of Azospirillum spp. has facilitated a better understanding of the mode of action of this plant-growth promoting bacterium and should help to improve its ability to stimulate plant growth and development. This review considers and discusses Agospirillum plasmids, promoter sequences, the isolation of Azospirillum mutants, the genetic transformation of Azospirillum, the transfer of foreign genes into Azospirillum by conjugation and the Azospirillum genes that have been isolated and characterized. The Azospirillum genes that are discussed include genes involved in nitrogen fixation, plant root attachment, phytohormone biosynthesis, tryptophan biosynthesis, carbon metabolism and a few other less well characterized processes. Received: 11 December 1997     

Defoliation effects on Plantago lanceolata resource allocation and soil decomposers in relation to AM symbiosis and fertilization

Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.     

Effects of low temperature and shade on relationships between nodulation,vesicular-arbuscular mycorrhizal infection,and shoot growth of soybeans

The effects of low temperature and reduced light on a Glycine-Bradyrhizobium-Glomus spp. symbiosis were examined in pot experiments. Soybean plants, Glycine max L. Merr. cv. Tachiyutaka, were grown with N fertilization or inoculation with Bradyrhizobium japonicum plus P fertilization or inoculation with Glomus mosseae in the glasshouse. After the flowering stage, half the pots with soybean plants were subjected to low temperature (15°C 14h/13°C 10 h) with light reduced by shading. At 0, 7, 16, and 28 days after the application of the treatments, the growth, nodulation, vesicular-arbuscular mycorrhizal (VAM) infection and the N and P contents of the soybean plants were measured. In all symbiont-fertilization combinations, the low-temperature treatment reduced the production of dry matter by the soybeans. Nodulation (weight and number) was slightly reduced by this treatment but the proportion of larger nodules was increased. The root length infected by the VAM fungus was little affected by the low-temperature treatment. Both the nodule weight and the infected root length were linearly related to shoot dry weight regardless of treatment and of the symbiont-fertilization combination used. These results suggest that the growth of the symbionts on the root was in balance with the shoot growth of the host, irrespective of climatic conditions, and imply a considerable degree of host control. P inflows to root systems were greatly affected by low-temperature treatment regardless of the symbiont-fertilization combination. This suggests that a simple comparison of P inflows between mycorrhizal and non-mycorrhizal plants may give misleading information on the effects of low temperature or reduced light conditions on P uptake by mycorrhizal plants.     

Effectiveness of two arbuscular mycorrhizal fungi on concentrations of essential oil and artemisinin in three accessions of Artemisia annua L.

A field experiment was conducted to study and compare the effectiveness of two arbuscular mycorrhizal fungi (AMF), Glomus macrocarpum (GM) and Glomus fasciculatum (GF) on three accessions of Artemisia annua. The AM inoculation significantly increased the production of herbage, dry weight of shoot, nutrient status (P, Zn and Fe) of shoot, concentration of essential oil and artemisinin in leaves as compared to non-inoculated plants. The extent of growth, nutrient concentration and production of secondary plant metabolites varied with the fungus–plant accession combination. The mycorrhizal dependency of the three accessions was related to the shoot: root ratio. Comparing the two fungal inoculants in regard to increase in essential oil concentration in shoot, the effectiveness of GF was more than that of GM. While in two accessions, GM was more effective in enhancing artemisinin concentration than GF. Increase in concentration of essential oil was found to be positively correlated to P-status of the plant. Conversely, no correlation was found between shoot-P and artemisinin concentration.     

Interactions of some nematicides with Azospirillum lipoferum and the growth of Zea maize

The possible interaction of four nematicides (Terbufos, Carbofuran, Fenamiphos, and Aldicarb) with Azospirillum lipoferum and growth of two Zea maize cultivars was studied in a greenhouse experiment. Application of nematicides, Fenamiphos in particular, resulted in higher plant length, dry matter production and N yield over the nematicide-untreated plants. Azospirillum spp. inoculation stimulated the growth of nematicide-treated Z. maize. Among the nematicides used, Carbofuran and Aldicarb inhibited the nitrogenase activity on plant roots more seriously than Fenamiphos and Terbufos. Generally, the inhibition percentages in acetylene reducing activity in soil of inoculated treatments were lower (14.4 - 61.8%) than those reported for the uninoculated ones (21.4 - 73.9%). Soil, irrespective of treatment, regained a part of its normal N₂-ase activity with time. Field concentrations of all nematicides showed different inhibitory effects on N₂-ase activity of Azospirillum spp. in culture medium, such effects increased with increased doses (10- and 100- fold) and incubation periods (10 days). The contribution of Azospirillum spp. to the N economy of soil treated with nematicides is discussed.     

分室磷添加下菌根对滇池流域红壤间作玉米生长及磷素利用的影响

随着全球范围内磷矿资源短缺问题的日益严重,间作或菌根技术强化作物对土壤磷(P)的利用及增产增收的效应受到越来越多的关注。通过三室隔网盆栽模拟试验研究了分室磷处理[不添加磷(P0)、添加有机磷(OP50)、添加无机磷(IOP50)]和根室不接种(NM)、根室接种丛枝菌根真菌Glomus mosseae(GM)对与大豆间作的玉米的生长及磷素利用的影响。研究结果表明:所有复合处理中,以间作?GM?IOP50组合处理下的玉米根系最短和地上部生物量最高;OP50处理下,间作玉米的菌根侵染率显著高于单作处理。间作条件下,无论分室磷添加与否,接种GM处理的玉米地上部生物量明显高于NM处理;接种GM处理的玉米根系生物量和株高均显著高于NM处理,且根系生物量以间作?GM?OP50组合处理下最高。接种GM条件下,P0、IOP50、OP50处理下的间作植株生物量较单作处理分别提高45.98%、111.33%、33.56%。单作条件下,无论分室磷添加与否,接种GM处理的玉米地上部磷含量均显著高于NM处理;无论何种种植模式及分室磷添加与否,接种GM处理的植物根系磷含量均显著高于NM处理。无论磷添加与否,间作?GM组合条件下的玉米地上部磷吸收量均显著较高,其中IOP50处理下的地上部磷吸收量显著高于OP50处理。间作?GM组合条件下,IOP50处理玉米根系的磷吸收效率均显著高于OP50处理。可见,接种GM、分室磷添加和间作各自在一定程度上促进了玉米的生长。综合菌根侵染、生物量及磷含量与吸收量、磷吸收效率等指标,所有复合处理中以间作?GM?IOP50组合对玉米地上部的促生作用最好,玉米磷素吸收最多,可望有效强化滇池流域红壤坡耕地磷素的利用。     

Vigna radiata var. GM4 Plant Growth Enhancement and Root Colonization by a Multi-Metal-Resistant Plant GrowthPromoting Bacterium Enterobacter sp. C1D in Cr(VI)-Amended Soils

Contamination of agricultural soils by heavy metals has become a major concern due to their toxic effects on plant growth, symbiosis and consequently the yields of crops. In the present study, to enhance plant growth in Cr(VI)-amended soils, novel metalresistant plant growth-promoting bacteria (PGPB) were isolated from a soil contaminated with industrial waste effluent. One of the bacterial isolates, identified as Enterobacter sp. C1D by 16S rRNA gene sequencing, was found to be multi-metal resistant in nature with excellent plant growth-promoting (PGP) traits. Mung bean (Vigna radiata var. GM4) inoculation with Enterobacter sp. C1D significantly (P < 0.01) increased root and shoot length, shoot and root weight, and chlorophyll content in a range of Cr(VI) treatments. Plant tolerance towards Cr(VI) measured as effective concentration showed higher values with Enterobacter sp. C1Dtreated plants compared to un-inoculated plants. Root colonization study was also carried out using green fluorescence protein-labeled Enterobacter sp. C1D under a hydroponic system. Confocal laser scanning microscopy of the plant roots showed heavy bacterial loads on the surface of the plant root specifically at the root tip and the point of root hair/lateral root formation. The results of PGP traits showed that elevated indole acetic acid levels and 1-aminocyclopropane-1-carboxylate deaminase activity enabled Enterobacter sp. C1D to enhance V. radiata growth in Cr(VI)-amended soils, whereby it significantly increased plant tolerance towards elevated Cr(VI) concentrations.     

Interrelationships between growth and nutrient uptake in alfalfa and corn

Nutrient requirements o£ plants during their various phases of growth are affected by several internal and external factors. The changes in rate of uptake by root with age are an important factor to meet the increasing plant demand for nutrients. Nutrient culture experiments were carried out under controlled greenhouse conditions with corn (Zea Mays L.) and alfalfa (Medicago sativa L.) to investigate the relationship of stage of growth to changes in plant parameters and nutrient uptake properties. With advancement of age. both plant species increased their ambient growth medium pH towards neutrality. With increasing age in alfalfa there was very little change in observed S:R ratio and root growth rate. On the other hand in corn plants the S:R ratio increased and growth rate for root and shoot decreased with age. Alfalfa contained higher concentrations of N, K, Na, and Ca than corn; while ion concentrations in both crops decreased with plant age. At all stages of growth, alfalfa absorbed less nutrients than corn. The rates of nutrient influx, I_n in both the crops showed various degrees of correlation with age and rate of shoot growth. In corn. I_n for ions reached a maximum at 25 days growth; whereas, in alfalfa, I_n reached maximum at 30 days of growth. The differences in influx rates for different ions in the two species are probably due to the difference in development of shoot and root parameters and shoot demand for the ions.     

Effect of mineral fertilizer,pig manure,and <Emphasis Type="Italic">Azospirillum rugosum</Emphasis> on growth and nutrient contents of <Emphasis Type="Italic">Lactuca sativa</Emphasis> L.

Benefits from the application of plant growth-promoting bacteria in agriculture largely depend on the complex interactions between several factors including the nature of fertilizers selected. This study was designed to determine the fine tuning between the inoculated bacteria and different fertilizers and their effect on the growth of lettuce plants (Lactuca sativa L.). Plant growth promotion by a novel species of the genus Azospirillum, namely A. rugosum IMMIB AFH-6, was tested by biochemical, bioassay, and greenhouse studies. The treatments used in the greenhouse study were; unfertilized control (Blank), half recommended dose of chemical fertilizer (1/2CF), full recommended dose of chemical fertilizer (1CF), pig manure fertilizer (PMF), pig manure fertilizer + half recommended dose of chemical fertilizer (PMF + 1/2CF), and pig manure fertilizer + full recommended dose of chemical fertilizer (PMF + 1CF). All these treatments when inoculated with A. rugosum IMMIB AFH-6 inoculation were, respectively, In-Blank, In-1/2CF, In-1CF, In-PMF, In-PMF + 1/2CF, and In-PMF + 1CF. Significant increase in plant biomass and shoot N, P, Ca, and Fe was shown in the In-Blank treatment. Plant growth in soil amended with PMF and A. rugosum IMMIB AFH-6 was significantly lower than in soil treated with the chemical fertilizer, but inoculation combined with chemical fertilizer significantly elevated the plant biomass. The In-PMF + 1/2CF treatment showed the highest yield. A. rugosum IMMIB AFH-6 facilitated the accumulation of trace minerals in higher concentrations when PMF was combined with 1CF. To examine the benefits of inoculation by A. rugosum IMMIB AFH-6, we have proposed a new type of data analysis which considers both biomass and nutrient content of plants. This new type of analysis has shown the importance of the mineral content of plant.